The present invention relates to a process for the consolidation of geological formations, said process being in particular applicable to reservoirs containing oil or gas, in order to eliminate inrushes of sand into wells traversing little or unconsolidated sandy formations. In more general terms, this process can be used for locally consolidating permeable formations.
The prior art is illustrated by U.S. Pat. No. 3,208,226 describing a ureaformaldehyde system for stabilizing soil and making the latter impermeable to water.
Various methods have already been proposed for preventing inrushes of sand into new wells or for treating wells giving rise to inrushes of sand, during the working of oil or gas deposits.
One method consists of injecting into the geological formation a liquid resin which, on polymerizing, creates a bond between the sand grains. A chemical method of this type has an arbitrary efficiency, because the injected resin polymerization reaction is essentially dependent on the conditions prevailing in the well at the said formation and the characteristics of the latter. Consequently such a method does not make it possible to check the degree of advance of the chemical reaction. There is consequently either a risk of an inadequate consolidation of the formation if the degree of polymerization of the resin is inadequate, or a risk of an excessive reduction of the permeability or even a complete clogging or blocking of the geological formation if an excessive polymer quantity is retained in certain pores.
In order to obviate this problem, French Patent 2 474 558, corresponding to U.S. Pat. No. 4,370,078, describes a process in which the polymerization reaction takes place between a liquid chemical agent containing appropriate catalysts put into place around the well to be treated and an injected oxidizing gas.
The circulation of gas following the putting into place of the polymerizable agent ensures that the permeability is maintained. The liquid organic mixture contains a polyethylene compound and a catalyst, so that oxidizing polymerization reactions lead to the consolidation of the medium without it being proved necessary to preheat the formation. However, this process requires the use of an oxygen-inert gas mixture, not necessarily always available. Moreover, the oxidizing gas quantity must be limited so that, as a result of the heat given off by the oxidation reaction, the temperature does not reach values above 350.degree. C., where the polymerized product would be subject to deterioration by combustion.
French Patent 2 575 500, corresponding to U.S. Pat. No. 4,685,836, describes a process in which the polymerization reaction of a liquid chemical agent containing appropriate catalysts and put into place around the well to be treated occurs under the action of a chemically inert, hot gaseous mixture. The circulation of gas following the putting into place of the polymerizable agent also maintains the permeability. However, this process requires the injection of a gaseous mixture having a temperature between 150.degree. and 325.degree. C., i.e. a value well above the temperatures generally encountered in reservoirs containing oil or gas.